Hollow fibers or microtubes of different materials can be used in many applications, depending on the hollow fiber material properties. Hollow fibers can be used in mass transfer devices, if the walls of the hollow fibers are permeable, and as heat transfer devices if the walls of the hollow fibers are heat conductive. Because hollow fibers are small, their thin walls pose relatively little barrier to heat and mass transfer between the inside and outside of the hollow fiber. It also becomes possible to package a large surface area for heat and mass transfer in relatively small volumes by densely bundling multiple hollow fibers into small packages. Examples of hollow fiber bundles used in heat and mass transfer include commercially available blood oxygenators which comprise a mass transfer portion with gas permeable hollow fibers, and a heat transfer portion with a heat conducting hollow fibers.
Montoya U.S. Reissue patent application Ser. No. 11/175,104, filed Jul. 5, 2005, now RE 41,870, issued Oct. 26, 2010, describes a method for forming hollow fiber bundles using a dissolvable core. The entire contents of this application are incorporated herein by reference, as some of the methods and descriptions therein may have utility in the present application, or may be useful in combination herewith. The method in the prior application can become time consuming to practice when the ratio of the diameter of the hollow fibers to the length of the bundle becomes very small, because it becomes increasingly slower to remove the dissolved support through small diameter and long passageways. Moreover, there are applications where the potential of trace residues of the support material or the solvent are not desirable in the resulting hollow fibers. In an effort to overcome these limitations, the following method for forming hollow fiber bundles comprising the following steps is presented.